To promote warming-up of an engine, an engine cooling device configured to restrict circulation of cooling water during the warming-up has been known (see PTL 1, for example).
An engine cooling device described in PTL 1 includes: a cooling water pump configured to receive driving force of an engine to supply cooling water to a water jacket provided in an engine main body; an external passage through which the cooling water having flowed out from the water jacket is guided to a heater core and an EGR cooler to be returned to the cooling water pump; a flow control valve provided in the external passage; an exit water temperature sensor configured to detect a temperature of the cooling water flowing out from the water jacket to the external passage; and an entrance water temperature sensor configured to detect a temperature of the cooling water flowing from the external passage into the water jacket.
When the water temperature detected by the exit water temperature sensor at the time of warming-up of the engine is less than a predetermined temperature, the cooling device stops driving of the water pump to stop circulation of the cooling water in the external passage and the water jacket. When the water temperature detected by the exit water temperature sensor becomes the predetermined temperature or more, the cooling device drives the water pump to start the circulation of the cooling water. When starting the circulation of the cooling water, the cooling device performs a control operation of decreasing an opening degree of the flow control valve as the water temperature detected by the entrance water temperature sensor decreases.
According to the cooling device described in PTL 1, when starting the circulation of the cooling water, the low-temperature cooling water accumulated in the passage gradually flows into the water jacket by controlling the opening degree of the flow control valve. Therefore, a steep temperature decrease of a cylinder bore due to the flow of a large amount of low-temperature cooling water into the water jacket can be suppressed.